Driving current crucial in blue diode failures

12 Jun 2008

An extensive analysis of blue laser diode degradation has found that control of crystal quality is the key to making the devices more reliable.

Better control of crystal quality is essential for improving blue laser diode reliability, according to a study by Panasonic and a team at the University of Padova, Italy. They found that the degradation process in these lasers is activated electrothermally, and not by any optical or straightforward heating mechanisms.

"The most important driving force for the degradation of blue laser diodes is driving current," commented Matteo Meneghini from the Padova laboratory. "The dependence is almost linear."

The Padova team found that the applied optical field did not influence the diode's degradation characteristics. Similarly, storing the lasers at 180 °C for 100 hours without any electrical bias had only a marginal effect on their reliability.

Until now it has not been clear how operating conditions impacted the performance of InGaN-based diodes like those employed in Blu-ray disc players and the PlayStation 3 console. Armed with the knowledge that it is specifically electrothermal stress that causes laser diodes to fail over time, the team is now looking more closely at the defects present in the semiconductor material to find ways to improve device lifetimes.

"Homoepitaxial growth represents one of the best strategies to preserve sample quality," said Meneghini. "The dislocation density must be reduced to guarantee long lifetime. Furthermore, the optimization of the growth conditions used for the active layer can lead to a reduced defect concentration, with corresponding improvement of device reliability."